These studies are designed to test the potential benefit of dietary n-3 fatty acids in reducing the frequency of thrombo-occlusive failure of arterial venous grafts in hemodialysis patients. The study exists in two phases. The first will compare the efficacy and feasibility in using either 0.1 or 0.3 g/kg per day of n-3 FAs versus an olive oil control in modifying the platelet function. Upon completion of the first phase, a controled clinical trial is planned using the chosen dose of n-3 FAs. The primary outcome will be the occurence of arterial venous graft failure over three years in a cohort of patients randomized to the n-3 FAs regimen or to olive oil treated control group.